1. Field of the Invention
The invention relates to a method of manufacturing a semiconductor device and an end point detection of dry-etching of an insulation film.
2. Description of the Related Art
Conventionally, a semiconductor process includes a process of dry-etching an insulation film formed on a semiconductor substrate to expose the semiconductor substrate. In this case, there is a problem such that the semiconductor substrate is damaged by being over-etched and the transistor characteristics are degraded. In order to prevent this problem, it is important to minimize the over-etching amount by detecting an etching end point accurately.
As a known method of detecting an end point of dry-etching, there is a method of detecting an end point based on a change of emission intensity (an emission amount) of a specific spectral line of plasma that is observed during dry-etching. In detail, in the case described above, as the etching of the insulation film to be etched is started, constant emission intensity is obtained by the etching of the insulation film. When the semiconductor substrate under the insulation film is then exposed and etched, the emission intensity changes. Therefore, the end point of the etching is detectable based on the difference of the levels of the emission intensity.
In the method of detecting the end point described above, however, when the area of the semiconductor substrate (an active region) to be exposed under the insulation film is small, the emission intensity of the specific spectral line of plasma is too small to distinguish the levels of the emission intensity.
In particular, when insulation films having different thicknesses are dry-etched simultaneously, the etching needs to be stopped by end point detection at the time when the semiconductor substrate under the thicker insulation film is exposed. In detail, after the etching is started, the thinner insulation film is removed by the etching to expose the semiconductor substrate under the thinner insulation film first. At this time, the thicker insulation film still remains. The thicker insulation film is then removed by the etching to expose the semiconductor substrate under the thicker insulation film.
Since the semiconductor substrate under the thinner insulation film is etched for a longer time, it is important to minimize the over-etching amount. However, it is difficult to perform such end point detection accurately by the method of detecting the end point described above.